Physicians make use of catheters today in medical procedures to gain access into interior regions of the body to ablate targeted tissue areas. For example, in electrophysiological therapy, ablation is used to treat cardiac rhythm disturbances. During these procedures, a physician steers a catheter through a main vein or artery into the interior region of the heart that is to be treated. The physician places an ablating element carried on the catheter near the cardiac tissue that is to be ablated. The physician directs energy from the ablating element to ablate the tissue and form a lesion. Such procedure may be used to treat atrial fibrillation, a condition in the heart in which abnormal electrical signals are generated in the endocardial tissue.
Ablation catheters typically have an elongated shaft carrying an electrode at its distal end. Lesions of different shapes and sizes may be formed by choosing a suitable electrode shape or size, and/or by manipulating the position of the electrode at the distal end of the catheter. An ablation catheter may also have a steering mechanism for steering its distal end, which is beneficial because it allows a physician to steer the catheter through veins and vessel junctions. It also allows the physician to accurately position the electrode carried at the distal end at a target site to be ablated. Steerable ablation catheters have been described in U.S. Pat. Nos. 6,033,378 and 6,485,455 B1, the disclosures of which are expressly incorporated by reference herein.
Torquable catheters have also been described in U.S. patent application Ser. No. 07/657,106, filed Feb. 15, 1991, the disclosure of which is hereby incorporated by reference in its entirety. Such a catheter provides a torsional stiffness such that when a physician applies a torque at a handle at the proximal end of the catheter, a corresponding torquing force is transmitted to the distal end of the catheter. This transmitted torquing force allows the physician to press the electrode against a tissue surface by torquing the distal end of the catheter.
During use of an ablation catheter, the electrode delivering ablation energy may overheat, thereby causing tissue charring and preventing formation of a deeper lesion. This may negatively affect the ablation catheter's ability to create a desirable lesion. An overheated electrode may also cause healthy tissue adjacent the target site to be heated. Furthermore, an overheated electrode may cause blood to be heated, thereby creating an undesirable embolism. As such, an ablation catheter that is capable of cooling an electrode is very desirable. Systems and methods for ablating tissue using actively cooled electrodes have been described in U.S. Pat. No. 5,800,432, the entire disclosure of which is expressly incorporated by reference herein.
Ablation catheters that have cooling capability may have a fluid delivery tube for delivering a cooling fluid to an electrode during use. If not designed or constructed properly, the fluid delivery tube may kink or buckle during use, especially if the ablation catheter has steering or torquing capability.
Thus, there is currently a need for an improved steerable/torquable ablation catheter that is capable of cooling an electrode tip during use, while preventing the fluid delivery lumen from kinking or buckling when the catheter is bent, e.g., during steering or torquing operations.